Ceramic Processing. Engineering Materials. 7/15/2009 Ceramic Processing/S.Rattanachan 1

Transcription

1 Ceramic Processing Engineering Materials 7/15/2009 Ceramic Processing/S.Rattanachan 1

2 Ceramic Processing Ceramic powders/raw materials + Additives Mixing Forming Firing Densification Sintering Vitrification Drying 7/15/2009 Ceramic Processing/S.Rattanachan 2

3 Additives of ceramics Binder: ก Lubricant: Plasticizer: ก ก Deflocculant: ก Dopants: ก 7/15/2009 Ceramic Processing/S.Rattanachan 3

4 Shape-Forming Processes Pressing Uniaxial Isostatic Hot pressing Hot isostatic pressing Slip casting Drain casting Solid casting Tape casting Doctor blade Waterfall Plastic forming Extrusion Roll forming Roller head Injection molding 7/15/2009 Ceramic Processing/S.Rattanachan 4

5 Uniaxial Pressing Free-flowing Powder containing binder, moisture, lubricant This cycle repeats typically 6 to 100 times per minute. Presses have a capacity from 1 to 20 tons. Process steps: Preparation Filling Compression Ejection Recycle 7/15/2009 Ceramic Processing/S.Rattanachan 5

6 Dry pressing Dry, Semidry or dust pressing 0 4 % moisture powder Products: electrical parts (capacitor, substrate), Bricks 7/15/2009 Ceramic Processing/S.Rattanachan 6

7 Isostatic pressing Cold isostatic pressing (CIP) Pressure from multiple directions high uniformity the walls of die deform and transmit the pressure uniformly to the powder. Process steps: powder is sealed in a water-tight die Sealed die is immersed in a liquid contained in a high pressure chamber seal the chamber Increase pressure of the liquid by hydraulic pumping release pressure remove die Products from CIP 7/15/2009 Ceramic Processing/S.Rattanachan 7

8 Hot isostatic pressing (HIP) near-net shape and high density Work pieces are heated and an inert gas, generally argon, applies uniform pressure. The temperature, pressure and process time are all controlled to achieve the optimum material properties. 7/15/2009 Ceramic Processing/S.Rattanachan 8

9 Slip casting Slip (Ceramic particles suspended in water) is casted into porous plaster molds. Complex shapes of thin uniform thickness Process steps: Slip preparation Filling mold Draining Remove mold trimming and drying 7/15/2009 Ceramic Processing/S.Rattanachan 9

10 Tape casting:doctor blade Products: substrates and packages for electronics Thin sheets in large quantity and low cost Slip contains about 50 vol% organic binder Process steps: Slip preparation de-airing tape casting drying machining and finishing 7/15/2009 Ceramic Processing/S.Rattanachan 10

11 Plastic forming: Extrusion Mixture of powder and additives are deformable under pressure. 25 to 50 vol% organic additive. Products: Dinnerware. Furnace tubes, pipe, bricks, tubular, catalyst support Process steps: Powder sizing Batch formulation Mixing Extrusion Drying Densification 7/15/2009 Ceramic Processing/S.Rattanachan 11

12 Injection molding Mixture of the ceramic powders with a thermoplastic polymer plus a plasticizer, wetting agent and anti-foam agent. Products: any complex shapes Process steps: mixture preparation preheat in the barrel Press the heated materials injection Release part from die Extraction of organics Densification 7/15/2009 Ceramic Processing/S.Rattanachan 12

13 Drying Evaporation from a free water surface: depend on the air temperature, air velocity, water content of air and water temperature Drying rates of ceramic body: Dark to light Rate of water loss in drying moist clay 7/15/2009 Ceramic Processing/S.Rattanachan 13

14 Densification /Sintering A removal of pores between the starting particles -> shrinkage -> strong bonding 7/15/2009 Ceramic Processing/S.Rattanachan 14

15 Stages of sintering 1 st stage (initial) Rearrangement Neck formation 2 nd stage (intermediate) Neck growth Grain growth High shrinkage Pore phase continuous 3 rd stage (final) Grain growth Discontinuous pore phase Grain boundary pores eliminated 7/15/2009 Ceramic Processing/S.Rattanachan 15

16 Microstructure after sintering Silicate ceramic: porcelain Closed pores Grain boundary Advanced Ceramics grain 7/15/2009 Ceramic Processing/S.Rattanachan 16 Intergranular pores

17 Phase diagram Mullite 3Al 2 O 3.2SiO 2 Mullite melts inconguently at 1890ºC. Refractory ceramic materials 7/15/2009 Ceramic Processing/S.Rattanachan 17

18 Glass 7/15/2009 Ceramic Processing/S.Rattanachan 18

19 Glass and crystalline Glass: ไม ตกผล ก ขนาดเปล ยนแปลงอย างช าๆขณะเย นต ว ม Tg (glass transition temperature) Crystal: ม การเปล ยนแปลงขนาดอย างรวดเร วท Tm (melting temperature) Changes in volume and temperature of a liquid cooling to the glassy or crystalline state. Reprinted with permission from Arun K. Varshneya, Fundamentals of Inorganic Glasses. Copyright 1994 Academic Press, Inc. 7/15/2009 Ceramic Processing/S.Rattanachan 19

20 Viscosity of silica glasses at varying temperature Viscosity decreases with T Impurity lower T deform T deform : soft enough to deform or work Melting point: glass is fluid Working point: viscosity is 104 P, glass is easily deformed. Softening point: viscosity is 4 x 107 P, glass may be handles without dimensional alterations. Annealing point: removed residual stress Strain point:tg will be above the strain point or below the strain point, fracture will occur before the onset of plastic deformation. 7/15/2009 Ceramic Processing/S.Rattanachan 20

21 Glass forming Pressing and blowing Optical fiber 7/15/2009 Ceramic Processing/S.Rattanachan 21 Drawing and fiber forming

22 Float glass 7/15/2009 Ceramic Processing/S.Rattanachan 22

23 Heat treating glasses Annealing: Thermal stress (the difference in cooling rate and thermal contraction between the surface and interior regions. Annealing heat treatment -> heat at annealing point and slowly cooled to room temperature. Hot cool Thermal stress 7/15/2009 Ceramic Processing/S.Rattanachan 23

24 Glass tempering Tempered glass is manufactured through heat-strengthening process. Strength of Tempered Glass is roughly four times of the regular float glass. Manufacturing Process Float glass is heated to 1150ºC with tempering oven and then rapidly cooled with highpressured air at high airflow rate. Heat-treated glass has increased resistance to impact, mechanical loads and thermal stress breakage as compared to regular float glass and heatstrengthened glass 7/15/2009 Ceramic Processing/S.Rattanachan 24

25 Toughened glass Sheets of glass are heated to about 700º C in a furnace, then chilled rapidly by cold air blown onto both surfaces. Toughened glass is four to five times stronger than float glass and, if broken, disintegrates into small fragments with dull edges which are unlikely to cause serious injury. Glass is now a primary construction material and can form 7/15/2009 Ceramic Processing/S.Rattanachan 25

26 Laminated glass PVB laminated :Two or more sheets of glass are bonded together with one or more layers of polyvinyl butyral(pvb), a plastic interlayer in sheet form. Its principle benefit being its performance under impact. The glass may fracture but any broken fragments will remain firmly bonded to the interlayer. Resin laminated glass is manufactured by pouring liquid resin into the cavity between two sheets of glass which are held together until the resin cures. This method is ideal for laminating glass having a heavily textured or patterned surface. Not all resin laminates have safety performance. They are principally used for decorative and accoustic purposes, where safety is normally of secondary importance. 7/15/2009 Ceramic Processing/S.Rattanachan 26